15 - Raised ICP

Question 1

What is ICP determined by and what are the normal values for this?

Answer 1

• Volume of blood, brain and CSF all enclosed within a rigid box

Question 2

How can we measure ICP?

Answer 2

• Lumbar puncture can be used to diagnose raised ICP and treat it

Question 3

What is the Monro-Kellie Doctrine?

Answer 3

• Increase in volume of one of the intracranial constituents (brain, blood or CSF) must be compensated by a decrease in the volume of one of the others
• e.g an intracranial mass, like a tumour, causes CSF and venous blood to be pushed out of the intracranial space as they are at the lowest pressure
• Due to skull being rigid plant pot

Question 4

What is cerebral perfusion pressure?

Answer 4

CPP = MAP - ICP

Normal CPP >70 mmHg

Normal MAP ~90mmHg

Normal ICP ~10 mmHg

Question 5

How does cerebral blood flow remain fairly constant despite changes in cerebral perfusion pressure?

Answer 5

- MAP increases then CPP increases, triggering cerebral autoregulation to maintain cerebral blood flow (vasoconstriction)

- ICP increases then CPP decreases, triggering cerebral

autoregulation to maintain cerebral blood flow (vasodilatation)

- If CPP falls below 50mmHg cerebral blood flow cannot be maintained as arterioles are maximally dilated

• Damage to brain can impair autoregulation

Question 6

What are some signs and symptoms of raised ICP?

Answer 6

(first three on right are Cushing’s triad)

- Headache: constant, worse in the morning and on bending/straining?

- Nausea and Vomiting

- Difficulty concentrating/drowsiness

- Diplopia

- Focal neurological signs

- Seizures

Question 7

What is Cushing’s reflex?

Answer 7

- Hypertension: rise in ICP so need rise in MAP to increased CPP

- Bradycardia: increase in MAP detected by baroreceptors causing reflex bradycardia by increasing vagal activity (can cause stomach ulcers due to vagal activity)

- Irregular breathing: compression of brainstem respiratory centres by herniation

Question 8

What are some causes of raised intracranial pressure in general?

Answer 8

• Too much blood within cerebral vessels
• Too much blood outside of cerebral vessels (haemorrhage)
• Too much CSF
• Too much brain
• Something else e.g tumour, cerebral abscess, idiopathic

Question 9

What are some examples of pathology involving too much blood within or outside of cerebral vessels that lead to a raised intracranial pressure?

Answer 9

• Raised arterial pressure (malignant hypertension)
• Raised venous pressure (e.g IVC obstruction by lung tumour)
• Extradural, subdural, subarachnoid haemorraghe
• Haemorraghic stroke
• Intraventricular haemorraghe

Question 10

Too much CSF can lead to a raised ICP, what are some causes of an increase in CSF?

Answer 10

- Congenital: cerebral aqueduct stenosis, neural tube defects, increased CSF production or decreased CSF absorption

- Acquired: meningitis, trauma, post subarachnoid haemorraghe, tumours compressing ventricular system like cerebral aqueduct

Question 11

What are some clinical signs of congenital hydrocephalus?

Answer 11

- Bulging head with head circumference increasing in diameter faster than expected

- Sunsetting eyes (compression of orbit and midbrain occulomotor)

Question 12

How is hydrocephalus managed?

Answer 12

Acute:

• Tap fontanelle with needle
• External ventricular drain (risk of infection and need to be inpatient but good if shunt doesn’t work and allows continuous monitoring)

Long-Term

• VA or VP shunt with valve to stop backflow (can be vulnerable to abdominal infections and may need surgical revision)

Question 13

What are the pathophysiological mechanisms of cerebral oedema?

Answer 13

- Vasogenic (breakdown of tight junctions)

- Cytotoxic (damage to brain cells)

- Osmotic (if CSF hypotonic)

- Interstitial (flow of CSF across ependyma into BBB)

Question 14

How does idiopathic intracranial hypertension (IIH) present?

Answer 14

• May present with headache and visual disturbance
• Usually middle aged obese females?
• Can be confirmed by raised opening pressure on LP
• Treat with weight loss and blood pressure control

Question 15

What do you need to do before you perform a lumbar puncture?

Answer 15

• Make sure there are no signs of intracranial pathology in a patient with suspected raised ICP as this can precipitate brain herniation

Question 16

What pathology can occur with the eyes when there is an increased intracranial pressure?

Answer 16

• Visual field defects
• Papilloedema
• Issues with acuity
• Accomodation issues (early sign)
• Pupillary dilation (late sign)

Question 17

What are the different types of herniation that can occur when there is a raised intra-cranial pressure?

Answer 17

- Tonsilar (coning - compresses medulla as cerebellar tonsils forced through foramen magnum)

- Subfalcine (cingulate gyrus pushed under falx cerebri, ACA can be compressed as passes over CC)

- Uncal (uncus goes through tentorial notch compressing midbrain, CNIII palsy and possible contralateral hemiparesis due to compression of the cerebral peduncles)

• Central downward herniation (medial temporal lobe down tentorial notch)

- External herniation through skull fracture or craniotomy

Question 18

How do we manage acute raised ICP to protect the brain?

Answer 18

- Airway and Breathing: maintain oxygenation and removal of CO₂

- Circulatory Support: maintain MAP and therefore CPP (avoid hypotension)

- Sedation, Analgesia and Paralysis: decrease metabolic demand and prevent coughs that may increase ICP further

- Head up tilt/Head of Bed elevation: improve cerebral venous drainage

- Temperature: prevent hyperthermia, therapeutic hypothermia might be beneficial

- Anticonvulsants: prevent seizures and reduce metabolic demand

- Nutrition and PPIs: improve injury healing and prevent stomach ulcers due to increased vagal activity

Question 19

How can we lower ICP after we have carried out brain protection measures?

Answer 19

• Mannitol or hypertonic saline (osmotic diuresis) then rehydrate orally
• Ventricualr drainage
• Decompressibe craniectomy (last resort)

Question 20

What are the two phases of the Monro-Kellie doctrine?

Answer 20

Question 21

When should you perform an urgent CT head?

Answer 21

Question 22

How can you tell if a subdural haemorraghe visible on CT is chronic or acute?

Answer 22

• Will appear much darker if chronic

- Less midline shift if chronic so neurological abnomalities may not be present

Question 23

Why do we want to hyperventilate a patient with raised ICP?

Answer 23

• CO₂ is a vasodilator so increase cerebral bood volumen and icpp

Question 24

What nursing care do we need for people when they are sedated due to raised ICP?

Answer 24

• Bowels (don’t want them straining)
• Urine
• Feeding
• Psyche

Question 25

What is the Chiari malformation?

Answer 25

Downward displacement of the medulla, fourth ventricle and cerebellum into the cervical spinal canal, as well as elongation of the pons and fourth ventricle. This type occurs almost exclusively in patients with myelomeningocele

Question 26

What is an anoxic brain injury?

Answer 26

Occurs when the brain is depleted of oxygen

Question 27

What is the criteria for brain death?

Answer 27